Certain deep hole drilling systems such as gun drills, single tube drilling systems, and double tube drilling systems are known in the art. These deep hole drilling systems may be used for drilling holes with a large depth to diameter ratio.
Solid carbide tooling is disadvantageous due to the need to regrind the cutting edges when worn, requiring removal of the tool from the drilling machine. Other problems with deep hole drilling tools include instability during drilling and at breakout. Tools having replaceable cutting heads have also been developed, which may use indexable cutting inserts. For example, there have been developed a single tube drilling system, or STS, used to drill holes having large depth to diameter ratios with improved penetration rates, hole size accuracy, and straightness as compared to gun drills. At the same time, such systems have various disadvantages, due to a single effective cutting edge, which causes significant stresses during machining. Additionally, such systems generally utilize one or more wear pads, which due to the configuration, tends to bear on the sides of the formed hole during cutting with significant force, such that the wear pad tends to cause hardening of the hole and embrittlement of the material. The wear pads on the tool body are used in an attempt to provide stability to the front of the drill by making contact with the inside wall of the hole just previously drilled. The use of a wear pad on the opposing side of a major diameter cutting insert has to be set at a diameter under the insert. This causes the tool to drill under or over size due to the imbalance of cutting forces and the inability to precisely balance these forces. Problems with past designs also include issues such as chips remaining in the hole between the body diameter and the inside of the hole or inability to effectively evacuate chips during drilling.
For many applications, there is a need for tooling that can effectively produce holes with a large depth to diameter ratio, and with high accuracy and in a cost effective manner. It would therefore be desirable to have a tool that provides stability and keeps the drilling on center. It would also be desirable to provide tooling that allows simple and flexible set-ups and adjustment to allow the tool to more effectively drill large depth to diameter ratio holes with high accuracy in metal workpieces.